1. Field of the Invention
The present invention relates to an image processing apparatus and an image shooting apparatus which easily correct distortion of an image, such as trapezoidal distortion.
2. Description of the Related Art
With advancement of digital cameras and cost reduction of storage type memories, studies have been made on applications in which digital cameras are not only used to shoot scenes and persons, but also shoot documents, such as papers and name cards, or what is written on a blackboard or so in a meeting, and digitally save those images in a personal computer or so for management.
In shooting a sheet using such a digital camera, the quadrangle of the sheet is deformed into a trapezoid. There is an image shooting system which corrects such trapezoidal distortion or keystone distortion. When a macrolens, a wide-angle lens or the like is used, the shape of a sheet is distorted into a barrel shape as shown in FIG. 13 due to the characteristics of those lenses. To acquire a high-quality image, such distortion should be corrected.
Various distortion correction methods are available to correct distortion originated from the lens characteristic. For example, because the distortion is generally distortion that is determined at the time of designing the lens, one possible method is to acquire points of an image having distortion which correspond to pixel coordinates of an ideal distortion-free image beforehand from the relationship between the pixel coordinates of the ideal distortion-free image and the pixel coordinates of the image having distortion, and acquire pixel data through interpolation or the like from the values of surrounding pixels.
This method however should perform pixel interpolation or so both in image extraction and projection correction and thus requires an interpolation operation twice. This increases degradation of an acquired image. When distortion is originated from the lens characteristic, correction should be carried out for each pixel, increasing the number of operations for correction, so that the overall processing takes time.